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Step 2.3 Evaluating Exposures for Possible Health Effects

After comparing the site-specific doses to the health guidelines, the health assessor selects those that need further evaluation. To conduct this further evaluation, the health assessor reviews studies on the chemical to see if the health effects evaluation supports a link between exposure to the chemical and a potential health effect.

Regardless of whether a chemical is being evaluated for cancer or noncancer effects, the health assessor's final step in the toxicologic evaluation is to review the relevance of the critical study, other substance factors, and site-specific health effects data for the chemical to determine whether site-specific exposures could result in health effects.

The health assessor then uses a health effects evaluation approach to make decisions about the potential health effects that could result from exposure.

Evaluating cancer effects

No one can predict who in a community might develop cancer because we do not understand why some people in a community develop cancer while other people do not. When we evaluate cancer health effects at communities where people are contacting chemicals from a hazardous waste site, we are only able to provide information on whether exposure conditions might or might not result in an increased risk of developing cancer.

The health assessor begins the cancer evaluation by estimating the site-specific cancer dose. Once the estimated dose is calculated, the health assessor compares the dose to the "cancer effect level," if one is available for the chemical being investigated. The cancer effect level is a dose of a chemical found to be associated with an increased number of cases of cancer in animal or human studies. Cancer effect levels are reported in ATSDR's toxicological profiles. The health assessor considers a number of factors about the study used for reporting the cancer effect level to decide how site-specific exposure conditions relate to study conditions.

With those considerations in mind, the health assessor might develop a "margin of safety" between the site-specific dose and the cancer effect level. For instance, the health assessor might determine that if the site-specific dose is 1,000 times less than the cancer effect level, then that would be a reasonable margin of safety to inform community members that they are not likely to have an increased risk of developing cancer because of their exposure. On the other hand, if the site-specific dose is only 10 times less than the cancer effect level, the health assessor might decide to research the literature further and conduct additional evaluation to determine whether community members are at increased risk of developing cancer.

Health assessors are also encouraged to use EPA's approach to calculate possible cancer risk. EPA's approach is very conservative; cancer risk is calculated on the chance that of 1,000,000 persons exposed to a chemical, one additional cancer might be found in the population as a result of exposure to the chemical. For small communities, a one-in-one-million cancer risk means that it is highly unlikely for anyone to develop cancer from their exposure.

The purpose of the review is to provide information to people in the community so that they may make informed decisions about their health care. Information will be provided about the types of cancer that have been associated with chemical exposures similar to those in the community. The information is also used to help health agencies and the community make decisions on other health actions that might be needed.